2025A&A...693A..49S

Context. Disks around intermediate mass stars called Herbig disks are the formation sites of giant exoplanets. Obtaining a complete inventory of these disks will therefore give insights into giant planet formation. However, to date no complete disk survey has been done on Herbig disks in a single star-forming region.
Aims. Our aim is to obtain the first complete survey of Herbig disks. Orion is the only nearby region with a significant number of Herbig disks (N=35) where such a survey can be carried out. The resulting dust mass distribution is compared to other dust mass distributions of disks around proto- and pre-main sequence stars in Orion. In addition, we ascertain whether previous Atacama Large Millimeter/submillimeter Array (ALMA) observations have been biased toward the most massive and brightest Herbig disks.
Methods. Using new Northern Extended Millimeter Array (NOEMA) observations of 25 Herbig disks, in combination with ALMA archival data of 10 Herbig disks, resulted in a complete sample of all known Herbig disks in Orion. Using uv-plane analysis for the NOEMA observed disks, and literature values of the ALMA observed disks, we obtained the dust masses of all Herbig disks and obtained a cumulative dust mass distribution. Additionally, six disks with new CO isotopolog detections are presented, one of which is detected in C¹⁷O. We calculated the external ultraviolet (UV) irradiance on each disk and compared the dust mass to it.
Results. We find a median disk dust mass of 11.7 M_⊕ for the Herbig disks. Comparing the Herbig disks in Orion to previous surveys for mainly T Tauri disks in Orion, we find that while ∼50% of the Herbig disks have a mass higher than 10 M_⊕, this is at most 25% for the T Tauri disks. This difference is especially striking when considering that the Herbig disks are around a factor of 2 older than the T Tauri disks. After a comparison to the Herbig disks observed with ALMA from a previous study, no significant difference is found between the distributions. We find a steeper relationship between the dust mass and external UV irradiation (slope of -7.6) compared to that of the T Tauri disks (slope of -1.3). Comparing our results to a recent SPHERE survey of disks in Orion, we see that the Herbig disks present the largest and brightest disks and have structures indicative of gas-giant formation.
Conclusions. Herbig disks are on average more massive compared to T Tauri disks. This work shows the importance of complete samples, giving rise to the need of a complete survey of the Herbig disk population.